The present invention relates to rotation sensors and, more particularly, to a silicon microgyro rotation sensor.
Navigational and inertial guidance systems for many types of craft often use data about the angular rate of motion of the craft to control the desired movement of the craft. One device which provides data about angular motion is the well known gyroscope. Gyroscopes, however, have many disadvantages. They are physically large and heavy, yet they must be built to extremely high accuracies at great cost, and they may be damaged by even low levels of shock and vibration. To minimize the effects of shock and vibration, they must be protected with heavy mounting devices, thus further increasing size, weight and cost. Furthermore, since critical moveable elements, such as bearings, usually wear with use, the gyroscopes must be frequently maintained to retain precision. Despite the frequent maintenance and high accuracy required, they still may have an error drift rate of fractions of a degree per hour.
Another type of angular motion sensor which attempts to overcome the disadvantages of traditional gyroscopes is disclosed in U.S. Pat. No. 4,899,587, issued to Juergen H. Staudte. That patent discloses an angular rate sensor comprising first and second tuning forks made of quartz. The stems of the forks are coupled together end to end along an axis of symmetry so that the tines face away from each other and lie in a plane. A mount is provided for attaching the dual fork structure to a support. Energy is provided to the tines of the first fork through a pair of electrodes coupled to an oscillator. The oscillator signals cause the tines of the first fork to vibrate in the plane. When the structure rotates about the axis of symmetry, a coriolus force causes the tines of the second fork to vibrate in a direction normal to the plane. The vibratory motion of the tines of the second fork is sensed with output electrodes for providing a signal indicating angular motion about the single axis.
Unfortunately, the electronics required for driving and sensing the vibratory motion of the forks is very complex and difficult to extract. The device is extremely susceptible to acoustic and vibrational interference, and the piezoelectric properties of quartz make the device very sensitive to stray capacitances. The support mounting for the fork structure creates unwanted stresses and points of failure, and the temperature anomalies of quartz create other electrical and mechanical difficulties. Finally, each device can sense rotation along only a single axis.